New synthesis strategies allowing to obtain materials of well-defined porosity in a very wide range, from microporous materials to macroporous materials to hierarchical porosity materials, i.e. having pores of several sizes, have known a very large development within the scientific community since the mid-90s (G. J. de A. A. Soler-Illia, C. Sanchez, B. Lebeau, J. Patarin, Chem. Rev., 2002, 102, 4093). Materials whose pore size is controlled are obtained. In particular, the development of synthesis methods referred to as “soft chemistry” has led to the elaboration of mesostructured materials at low temperature through the co-existence, in aqueous solution or in solvents of marked polarity, of inorganic precursors with structuring agents, generally molecular or supramolecular surfactants, ionic or neutral. Control of electrostatic interactions or through hydrogen bonds between the inorganic precursors and the structuring agent jointly linked with hydrolysis/condensation reactions of the inorganic precursor leads to a cooperative assembly of the organic and inorganic phases generating micelle aggregates of surfactants of uniform and controlled size within an inorganic matrix. This cooperative self-assembly phenomenon governed, among other things, by the structuring agent concentration, can be induced by progressive evaporation of a solution of reactants whose structuring agent concentration is lower than the critical micelle concentration, which leads to either the formation of mesostructured films in the case of a deposition on substrate (dip-coating technique) or to the formation of a mesostructured powder after atomization (aerosol technique) or draining of the solution. By way of example, patent U.S. Pat. No. 6,387,453 discloses the formation of mesostructured organic-inorganic hybrid films by means of the dip-coating technique, and these authors have furthermore used the aerosol technique to elaborate mesostructured purely silicic materials (C. J . Brinker, Y. Lu, A. Sellinger, H. Fan, Adv. Mat., 1999, 11, 7). Clearance of the porosity is then obtained by surfactant elimination, which is conventionally carried out by means of chemical extraction processes or by thermal treatment. Depending on the nature of the inorganic precursors and of the structuring agent used, and on the operating conditions applied, several families of mesostructured materials have been developed. For example, the M41S family initially developed by Mobil (J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T.-W. Chu, D. H. Olson, E. W. Sheppard, S. B. McCullen, J. B. Higgins, J. L. Schlenker, J. Am. Chem. Soc., 1992, 114, 27, 10834), consisting of mesoporous materials obtained using ionic surfactants such as quaternary ammonium salts, having a generally hexagonal, cubic or lamellar structure, pores of uniform diameter ranging from 1.5 to 10 nm and amorphous walls of thickness of the order of 1 to 2 nm, has been widely studied. Later, in order to increase the hydrothermal stability properties while developing acido-basicity properties relative to these materials, the incorporation of the element aluminium in the amorphous silicic framework by direct synthesis or post-synthesis processes has been particularly studied, the aluminosilicate materials obtained having a Si/Al molar ratio ranging between 1 and 1000 (S. Kawi, S. C. Shen, Stud. Surf. Sci. Catal., 2000,129, 227 ; S. Kawi, S. C. Shen, Stud. Surf. Sci. Catal., 2000,129, 219; R. Mokaya, W. Jones, Chem. Commun., 1997, 2185). The hydrothermal stability and acido-basicity properties thus developed by these aluminosilicates have however not allowed them to be used at an industrial stage in refining or petrochemistry processes, which has progressively led to the use of new structuring agents such as amphiphilic macromolecules of block copolymer type, the latter leading to mesostructured materials having a generally hexagonal, cubic or lamellar structure, pores of uniform diameter ranging from 4 to 50 nm and amorphous walls of thickness ranging from 3 to 7 nm. Unlike the dip-coating or aerosol techniques described above, the materials thus defined are not obtained through progressive concentration of the inorganic precursors and of the structuring agent within the solution where they are present, they are conventionally obtained by direct precipitation within an aqueous solution or in solvents of marked polarity by using the value of the critical micelle concentration of the structuring agent. Furthermore, synthesis of these materials obtained by precipitation requires a ripening stage in an autoclave and all the reactants are not integrated in the products in stoichiometric proportion since they can be found in the supernatent. Depending on the structure and on the organization degree required for the final mesostructured material, these syntheses can take place in an acidic medium (pH≈1) (WO-99/37,705) or in a neutral medium (WO-96/39,357), the nature of the structuring agent used also playing an essential part. The elementary particles thus obtained have no regular shape and they are generally characterized by a size above 500 nm. The mesostructured aluminosilicate materials thus obtained exhibit increased hydrothermal stability properties in relation to their homologs synthesized via other structuring agents, their acido-basicity properties remaining more or less similar (1<Si/Al <1000). Low Si/Al molar ratio values are however difficult to obtain because large amounts of aluminium are not readily incorporated in the material via these particular operating methods (D. Zaho, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson, B. F. Chmelke, G. D. Stucky, Science, 1998, 279, 548; Y. -H. Yue, A. Gédéon, J. -L. Bonardet, J. B. d'Espinose, N. Melosh, J. Fraissard, Stud. Surf. Sci. Catal., 2000,129, 209).